The application is for renewal of a grant that has supported a long-term investigation of mechanisms of nociception and antinociception. The eventual goal of the proposed studies is to learn how plastic changes in nociceptive responses lead to persistent pain and to develop new approaches for chronic pain therapy. The overall hypothesis of the present proposal is that nociceptive transmission in the spinal cord is regulated by protein kinases and phosphatases through phosphorylation and dephosphorylaion of synaptic receptors and of proteins involved in intracellular signal transduction pathways. The outcome of this regulation can be central sensitization (or conversely, long-lasting inhibition) of nociceptive neurons, such as spinothalamic tract (STT) cells, as well as changes in gene expression in nociceptive neurons. Central sensitization, which has been suggested to underlie secondary allodynia and hyperalgesia, is proposed to depend at least in part on postsynaptic changes in STT cells. Specific Aim 1 is to determine if different protein kinases are activated in STT cells and if different protein kinases contribute to differences in the responses of STT cells to innocuous and noxious stimuli, leading to different balances of allodynia and hyperalgesia. Specific Aim 2 is to determine if the induction of central sensitization, like long-term potentiation, depends on the activation of calmodulin and calcium/calmodulin-dependent kinase II (CaMKII). Specific Aim 3 is to determine if phosphorylation of amino acid receptors occurs in STT cells during central sensitization and to investigate how inhibition of CaMKII permits the expression of along-lasting inhibition. Specific Aim 4 is to determine if agents that alter central sensitization also alter the expression of inducible immediate, early genes and phosphorylation of constitutive transcription factors. The experimental approaches that will be used include the analysis of behavioral changes, electrophysiological recordings and pharmacological modulation of proteins involved in nociceptive signal transduction, and immunohistochemical and Western blotting studies, using antibodies to non-phosphorylated and phosphorylated proteins that contribute to the structure of glutamate receptors or belong to signal transduction pathways.